1. Field of the Invention
The present invention generally relates to wireless communication systems, and more particularly, to a Physical Downlink Shared CHannel (PDSCH) data transmission method.
2. Description of the Related Art
A Long Term Evolution (LTE) system supports a Frequency Division Duplexing (FDD) mode and a Time Division Duplexing (TDD) mode. FIG. 1 is a schematic diagram illustrating the structure of a frame in a TDD system. The length of each radio frame is 10 ms, with each radio frame divided into two half-frames of a length of 5 ms. Each half-frame consists of eight data time slots, each of which having a length of 0.5 ms, and three special time slots, i.e., Downlink Pilot Time Slot (DwPTS), Guard Period (GP) and Uplink Pilot Time Slot (UpPTS). The entire length of the three special time slots is 1 ms. Each sub-frame consists of two continuous time slots, that is, the kth sub-frame includes time slot 2k and time slot 2k+1.
The TDD system supports seven different uplink and downlink configurations. As shown in Table 1, D denotes a downlink sub-frame, U denotes an uplink sub-frame, and S denotes a special sub-frame consisting of the above mentioned three special time slots.
TABLE 1Config-switchingurationpointSub-frame numbernumbercycle01234567890 5 msDSUUUDSUUU1 5 msDSUUDDSUUD2 5 msDSUDDDSUDD310 msDSUUUDDDDD410 msDSUUDDDDDD510 msDSUDDDDDDD610 msDSUUUDSUUD
In order to increase the user's transmission rate, the LTE-Advanced (LTE-A) system of the LTE system has been introduced. In the LTE-A system, a wider bandwidth is obtained by aggregating multiple Component Carriers (CCs), i.e., through Carrier Aggregation (CA), and constitutes the uplink and downlink of a communication system to support the higher transmission rate. For instance, 100 MHz bandwidth may be obtained by aggregating five 20 MHz CCs. Here, each CC is called a cell. For a User Equipment (UE), a base station may configure the UE to work in multiple Cells, one of which is the Primary Cell (PCC or Pcell), and the others are called Secondary Cells (SCC or Scell).
According to a requirement in the LTE-A TDD system, multiple cells aggregated together adopt the same uplink and downlink configuration.
However, when the distance in the frequency domain among multiple cells on which Carrier Aggregation will be performed is large enough, these cells may adopt different TDD uplink and downlink configurations without interfering with each other. In addition, in some cases, an adjacent channel of each cell may have been deployed in a different uplink and downlink configuration (for example, the adjacent channel has different Time Division-Synchronous Code Division Multiple Access (TD-SCDMA) configuration). At this point, if these cells continue to adopt the same TDD uplink and downlink configuration, serious adjacent channel interference will be generated. Therefore, in subsequent studies of LTE-A, an important issue is how to effectively support the multiple cells on which Carrier Aggregation will be performed, wherein the multiple cells have different TDD uplink and downlink configurations.
In order to protect controlling signals under a Heterogeneous Network (Het-Net) scene, cross-carrier scheduling mode has been introduced. The cross-carrier scheduling refers to PDSCH data transmission in a cell that is scheduled by a Physical Downlink Control CHannel (PDCCH) sent in another cell. As shown in FIG. 2, PDCCH in cell schedules PDSCH data in cell2. Thus, when serious interference exists in cell2, a control channel of cell2 may be transmitted in cell1, so the control channel of cell2 is protected. The cell sending the PDCCH is known as a cell for scheduling, and the cell sending the PDSCH is known as a cell being scheduled.
According to the requirements in current 3GPP version 10, the cross-carrier scheduling of PDSCH refers to a PDCCH of a cell for scheduling a PDSCH of a cell being scheduled of which a sub-frame is the same as that of the PDCCH. Thus, when the TDD uplink and downlink configuration of the cell for scheduling is different from that of the cell being scheduled, especially when the downlink sub-frames of the cell being scheduled is not in a set of downlink sub-frames of the cell for scheduling, PDSCHs in part of downlink sub-frames of the cell being scheduled will be unable to be scheduled in cross-carrier manner due to the TDD uplink and downlink configuration of the part of downlink sub-frames that is different from that of the downlink sub-frames of the cell for scheduling.
FIG. 3 is a schematic diagram illustrating two cells adopting different TDD uplink and downlink configurations. In FIG. 3, the upper part is a schematic diagram illustrating a TDD uplink and downlink configuration of the cell for scheduling, and the lower part is schematic diagram illustrating TDD uplink and downlink configuration of the cell being scheduled. As can be seen from FIG. 3, according to above mentioned cross-carrier scheduling principle, sub-frame 3 and sub-frame 8 of the cell for scheduling can not schedule downlink sub-frame 3 and sub-frame 8 of the cell being scheduled in cross-carrier manner due to sub-frame 3 and sub-frame 8 of the cell for scheduling being uplink sub-frames.
As can be seen, when the existing PDSCH cross-carrier scheduling method is adopted to implement the PDSCH transmission, it may cause a problem in that PDSCHs in part of the sub-frames can not be scheduled. Thus, the peak rate of a terminal user is affected, and a requirement for higher throughput of the terminal user can not be satisfied.